fix(curriculum): change name of vairable from reserved keyword (#56636)

curriculum/challenges/english/07-scientific-computing-with-python/learn-encapsulation-by-building-a-projectile-trajectory-calculator/663353465bfb14259717da93.md

@@ -47,7 +47,7 @@ The method should return the correct output.
 ```js
 ({
     test: () => assert(runPython(
-        `str = """
+        `a = """
   x      y
   0   3.00
   1   3.90
@@ -65,7 +65,7 @@ The method should return the correct output.
 """
 ball = Projectile(10, 3, 45)
 g = Graph(ball.calculate_all_coordinates())
-g.create_coordinates_table() == str`
+g.create_coordinates_table() == a`
     ))
 })
 ```